Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$147.47	4.724%	$154.4365	$154.44	$154.45	$154.40
Purchase #2	$159.71	3.520%	$165.3318	$165.33	$165.35	$165.30
Purchase #3	$99.85	3.282%	$103.1271	$103.13	$103.15	$103.10
Purchase #4	$219.91	8.341%	$238.2527	$238.25	$238.25	$238.30
Purchase #5	$157.33	3.492%	$162.824	$162.82	$162.80	$162.80
Purchase #6	$60.25	10.108%	$66.3401	$66.34	$66.35	$66.30
Purchase #7	$26.40	4.562%	$27.6044	$27.60	$27.60	$27.60
7 purchase totals =	$870.92		$917.9166	$917.91	$917.95	$917.80